This could be the week that Apple chalks up its one-billionth iPhone application download, according to this post at MoCoNews. Principal Correspondent Tricia Duryee does the math and figures “about 100 apps are being downloaded every second-that’s 6,000 every minute, 360,000 every hour and 8.6 million a day.”

It’s a flood of apps that pegs the needle, and no doubt plays in favor of companies that recognized the potential of the Apple App Store early on. I’m thinking here of mobile ad marketplace AdMob, which just launched Download Tracking for iPhone applications, allowing advertisers to accurately monitor App Store conversion rates, (detailed in a separate post based on an exclusive briefing with Russell Buckley, AdMob VP Global Alliances); and Taptu, a mobile search company gearing up to solve the search/discovery problem in the “Touch Web” and become a leading App Store mobile ad network in the process (an ambitious plan I discuss tomorrow’s exclusive Q&A with Andreas Bernstrom, Taptu COO).

The iPhone has helped to unleash a new interest among consumers in the mobile Web, but it nonetheless represents a tiny subset of the total mobile market. To date Apple has sold 17 million iPhones worldwide (a total Nokia generally tops in a fortnight). Garter puts it in perspective: It concludes that smartphones account for a small percentage of handsets (11-12 percent of all handsets sold globally), and iPhones account for an even smaller percentage of total smartphones (8.2 percent of handsets sold globally).

Another keys data point comes from comScore. It reports that more than half (54 percent) of app users are in households making at least $75,000 per year. If your end-goal is about reaching a mass-market audience with apps, ads or marketing campaigns, you’re well-advised to think beyond the iPhone.

Before jumping on the iPhone bandwagon, we should also take a closer look at new stats from AdMob and Bango, numbers that both confirm and deny iPhone’s leading position.

First, the monthly AdMob Mobile Metrics Report.

It lists the top smartphones in its network (market share AdMob calculates “based on the percentage of requests received by a particular handset” for the ads its serves), and found that smartphones generated a whopping 33 percent of worldwide traffic in February 2009, up 26 percent from six months ago. The real surprise: iPhone generated 33 percent of all smartphone traffic worldwide and half (!) of all traffic in the U.S.

Wow (!), iPhone is where the action is – or so it seems…

New data from Bango, a provider of mobile analytics solutions, tells a different story. The Bango Top 20 handset list (likewise based on February stats) puts the Nokia 3110c in the number one spot; iPhone comes in at number 24 (!). By way of background,Bango data looks at the activities of major brands and businesses as their consumers browse to mobile websites (measured by Bango Analytics) and buy mobile content and services (as measured by Bango Payment).

How can iPhone be both a leader and a laggard?

As this well-written/researched post from mobiThinking points out: It depends on where you sit. AdMob counts the number of mobile adverts it serves to different types of handsets, not unique handsets. “So, if iPhone users surf more (aren’t the majority of iPhone users on unlimited data plans?), then iPhones go to the top. So, from AdMob’s perspective iPhone is indeed the only game in town.

Bango, because it can identify and track unique visitors to its customers’ sites, has correctly identified a diverse range of handsets browsing the mobile Web. It’s a more representative sample of the devices surfing the mobile Web, with smartphones accounting for 30 percent of handsets in the top 20.

My take: The existence of two conflicting views of the handsets that matter most (to advertisers/publishers) underlines the importance of employing analytics tools that provide a more holistic view of what customers do and the devices they use. Focusing only on the iPhone or only mass-market handsets is a sure-fire way to short change yourself and your customers. It takes two, baby!

But it’s not just about big-picture anayltics; it’s about how brands and publishers approach the mobile Web.

As Boris Fridman, Crisp Wireless CEO, points out (via the company newsletter): ” For everyone thinking about investing in an iPhone app, I say, kudos – but don’t do it at the expense of a mobile website.  Our recent Crisp Wireless Index shows that iPhone usage for mobile browsing across our network has grown significantly from 9.1 percent to 22.98 percent.  However, Blackberry browsing still holds a significant share at 23.98%. Furthermore, recent studies from Pinch Media show that as novelty wears off, iPhone app usage drops significantly after 90 days. Mobile has become a crucial channel that requires a multi-pronged approach.  Our own Tom Limongello recently stated it best in his blog post pointing out how maintaining a mobile or iPhone-optimized website to complement iPhone apps is key to maintaining discoverability and addressing a broader market.” (More from Crisp Wireless  in an exclusive interview next week.)

I’m reminded here of an interesting debate during a recent industry conference, a discussion I would like to open up to MSG readers. Does the popularity of the iPhone among this demographic and the continued hype around the iPhone (one that sees many companies invest in the iPhone as their only mobile play) combine at some level to create a new kind of iPhone-only affluent mobile Internet (as opposed to a mass-market mobile Internet for the rest of us)? What do YOU think? What’s more, is there a danger this will increase fragmentation and move us one giant step away from the One Web vision Steve Bratt, Chief Executive Officer, World Wide Web Consortium, outlines in this excellent presentation?

Disclaimer: AdMob has been an MSG supporter; Bango is an MSG supporter.